This invention relates to an assembly for sealing a sheet of covering material or covers onto containers. More particularly, the present invention relates to an improved method and assembly for sealing a sheet of material to a flange of a container in which the flange has an irregular surface or nonuniform thickness.
Containers for holding various products are often formed from paperboard or the like in a die press. The containers are formed from flat paperboard blanks which have been scored in predetermined areas to facilitate formation of the containers. The scored sections reduce the likelihood that the blank will tear as the container is formed. The containers are used to hold various products such as food.
Various types of automated systems are known for automatically filling containers moving along a predetermined path with a product such as food or the like. Individual containers which contain one or more servings of food and are sold either refrigerated or frozen are becoming increasingly popular. Such containers are typically processed on an assembly line, with the filling of the containers usually being accomplished with overhead buckets, funnels, or spouts that disburse a metered amount of the product into each individual container.
The containers are transported in metal container carriers along the assembly line in a predetermined direction. A roller chain or other suitable drive means is used to move the container carriers along the assembly line path. In some instances, a continuous sheet of material has been used to cover the containers. After the product is placed in the container, the sheet of material is sealed to the top of the containers and then cut. In other instances, individual covers may be placed on the containers before sealing. Packaging devices often use heat sealing assemblies to seal the sheet of material or covers to a flange of the containers.
Problems arise when attempting to seal the sheet of material to a top flange of the deep-drawn paperboard containers. Scored sections of the containers which are usually positioned at the corners of the containers have a thickness greater than the thickness of the nonscored regions. Difficulties arise when attempting to seal the sheet of material to the flange which has a nonuniform thickness.
One object of the present invention is to provide a method and apparatus to facilitate sealing of a sheet of material to a flange of a container when the flange has a nonuniform thickness.
According to the present invention, a method is provided for sealing a first material to a second material. The second material includes first regions having a first thickness and second regions having a second thickness greater than the first thickness. The method includes the steps of providing a support surface, providing a sealing head, and pressing the first material against the second material between the support surface and the sealing head. The method also includes the step of applying a first pulse from the sealing head to the first and second materials for a first predetermined duration to cause friction between the second regions of the second material and the first material. The method further includes the step of maintaining the sealing head in engagement with the first and second materials to clamp the first and second materials together after the first pulse ends so that the second regions of the second material bond to the first material. The method still further includes the step of applying a second pulse from the sealing head to the first and second materials for a second predetermined duration to cause friction between the nonbonded first regions of the second material and the first material to bond the first regions of the second material to the first material.
Ultrasonic pulses are used in the illustrated embodiment to seal the covering material to the flange of the containers. The ultrasonic sealing method advantageously increases the speed of sealing the covering material to the containers as compared to conventional heat sealing assemblies. In addition, as the covering material for sealing containers becomes more sophisticated, heat sealing techniques become less effective. Specifically, the cover material can be a fiberboard lid which is printed to look visually attractive. These fiberboard lids are typically somewhat insulated. Therefore, the use of heat to seal the fiberboard lid is limited by the insulation of the lid. In addition, heat can damage the inks used to print information on the lids. The ultrasonic sealing method of the present invention also permits the covering material to be sealed to the container flange through contaminants which may be on the flange or the covering material.
According to another aspect of the present invention, a container carrier is provided for supporting a container having an outer flange including first regions which have a first predetermined thickness, second regions which have a second predetermined thickness greater than the first predetermined thickness, and a top surface. The container carrier includes a carrier body having an upper surface and a lower surface. The container body is formed to include an aperture extending between the upper and lower surfaces for receiving the container therethrough. A portion of the upper surface of the carrier body adjacent the aperture is configured to abut the flange of the container to support the container in the carrier body. The portion of the upper surface has a first depth in first sections which underlie the first regions of the flange, and the portion of the upper surface has a second depth in second sections which underlie the second regions of the flange. The second depth is greater than the first depth so that the top surface of the flange lies substantially in a single plane.
Advantageously, the container carrier of the present invention permits the sealing assembly to distribute the energy from the sealing heads evenly across the surface of the flange, even in transition areas between the thick and thin regions of the material. This advantage is accomplished by matching the container carrier geometry with the geometry of the specific container. Subtle changes in the incline of the container flange can cause substantial differences in the energy distribution along the flange.
In the illustrated embodiment of the present invention, a support band is provided surrounding the aperture of the carrier for engaging the flange of the container. The support band concentrates the force from the sealing head on a smaller area of the flange which causes greater deformation of the container flange to improve the seal between the container flange and the covering material.
Additional objects, features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.